1. Field of the Invention
This invention relates to a resin cultivating base on which seedlings of aquatic plants and so on are planted and which is partially immersed in not only a stream, a natural or man-made river, lake and marsh but also in a waterway drawing the water from them and communicating with reservoirs such as water purifying tanks of a sewage disposal plant or the like. In this specification, the stream, river, lake, marsh and waterway will be collectively called the “waterway” hereinafter. Further, the invention relates to a water purifying device which is constituted by the foregoing resin cultivating base where vegetation is planted and raised in order to promote natural purifying capabilities of the waterway, and to a water purifying method.
2. Description of the Related Art
Water pollution has become a serious with waterways. A variety of proposals have been made in order to overcome this problem.
As one method of overcoming water pollution, it is conceivable that water is temporarily drawn from the waterway using a pump, is purified by oxidization resulting from contact with gravel, sand filtering, coagulation filtering, precipitation and so on, and is finally returned to the waterway. However, this method requires a large-scale water purifying plant, and a lot of labor and expense in order to maintain and manage the plant. Recently, various methods are being studied in order to purify water by promoting natural purifying capabilities of a waterway using a relatively simple method.
For promoting said natural purifying capabilities of a waterway, it has been proposed to root aquatic plants in a waterway so that the natural purifying capabilities of the waterway are promoted. Generally speaking, aquatic plants such as reeds usually grow very well in shallows which are 80 cm or less deep. However, since current waterways become very deep at river banks or lake sides due to bank protecting works, it is very difficult for the foregoing aquatic plants to grow naturally. In order to root the aquatic plants, foundation work has to be carried out on a relatively large scale, so that a foundation 81 is built using concrete, and a chamber 82 is provided on the foundation 81 as shown in FIG. 15. Then, coconut fiber 83 is filled in the chamber 82 so as to make a seed bed 80. In other words, the environment is improved for and enables growth of aquatic plants, which is effective in purifying the waterway. In this case, the foundation work is very expensive, and requires a lot of labor. Therefore, simple methods of promoting the natural purifying capabilities of the waterway have been studied recently.
Referring to FIG. 16, in one such method, a seed bed 80 is constituted by a mat 92 or the like, which is made of compressed and molded natural coconut shell, coconut chips, coconut carbon or the like. The mat 92 is covered by non-woven cloth or a net 91. Aquatic plants 70 are planted on the mat 92 as the seed bed, thereby forming a floating island. The floating island is placed in the waterway in order that the vegetation thereon promotes purification of the water. Referring to FIG. 17(B), an article comprises a string 96 as a core and loop yarns 97 wound around the string 96. A number of such articles are placed in the waterway so that microorganisms living in the water stick onto the loop yarns 97 and decompose organisms in the waterway, thereby purifying the waterway.
With the first mentioned method in which vegetation is raised on the seed bed 80 in order to purify the water, the mat 92 made of coconut fibers or made by processing coconut fibers used as the seed bed 80 is relatively expensive. Further, since each item of vegetation has very small purifying capabilities, a great number of mats 92 as the seed beds 80 should be provided in order to raise a great amount of vegetation and in order to purify the water to a certain degree. Therefore, this method is very expensive for performing water purification.
In order to demonstrate the water purification capabilities, the vegetation 70 should grow its roots 71 through which nutritious salt such as phosphorous, nitride and so on in the water are sucked. The voids of the seed bed 80 should be 80% or more in order to raise the roots 71 of the vegetation, and vegetation such as reeds and bulrush in particular. However, currently available seed beds 80 made of compressed coconut fibers or coconut shells usually have voids of 80% or less, and cannot sufficiently grow the roots 71 of the vegetation 70. On the other hand, the seed bed 80 made of coconut fibers or coconut shell and having voids of 80% or more cannot withstand weight of grown vegetation 70 such as reeds, and cannot effectively carry out its function.
For the foregoing reasons, the seed bed 80 with the vegetation growing thereon is used to improve the view at the waterside rather than to purify the water. The effect of water purification is only slightly accomplished as a side-effect.
As for the second mentioned method in which innumerable loop like cylindrical structures 95 are placed in the water, microorganisms living in the loop yams 97 decompose organisms therein; which purifies the water. If such loop like cylindrical structures 95 are placed on a riverbed along the flow of the waterway as shown in FIG. 17(A), only the water flowing on the riverbed comes across them. Therefore, a very limited amount of water can come into contact with the loop like cylindrical structures 95, which means that sufficient water purification effects cannot be expected.
On the other hand, if each cylindrical structure 95 is placed in the waterway along the depth thereof, it should be connected to the riverbed and a float 98 at its opposite ends as shown in FIG. 17(B). However, innumerable man-made floats 98 on the surface of the waterway may adversely affect the scenery.
Still further, fibers serving as homes for microorganisms may be preferably natural fibers having uneven surfaces and being comfortable rather than synthetic resin fibers having smooth surfaces. However, natural fibers tend to decay when they are used in the water for a long period of time.
Therefore, the present invention has been contemplated in order to overcomes the foregoing problems of the related art. Particularly, the invention is aimed at providing a resin cultivating base which has voids appropriate for raising aquatic plants such as reeds and bulrush and is durable for a long period of time in water, which are contradictory each other. Further, the invention provides a water purifying device composed of the foregoing resin cultivating base, and a method of purifying water in order to improve the environment around the waterway and comfort people by promoting the natural purifying capabilities of the vegetation planted on the resin cultivating base.